Hydroxyphenyl-piperazinyl-methyl-benzamide derivatives for the treatment of pain

ABSTRACT

Compounds of general formula I  
                 
 
     R 1  is selected from any one of pyridinyl, thienyl, furanyl,  
     imidazolyl, and triazolyl;  
     where each R 1  heteroaromatic ring may optionally and independently be further substituted by  1, 2  or  3  substituents selected from straight and branched C 1 -C 6  alkyl, NO 2 , CF 3 , C 1 -C 6  alkoxy, chloro, fluoro, bromo, and iodo. The substitutions on the heteroaromatic ring may take place in any position on said ring systems;  
     are disclosed and claimed in the present application, as well as separate enantiomers of the compounds and salts and pharmaceutical compositions comprising the novel compounds and their use in therapy, in particular in the management of pain.

FIELD OF THE INVENTION

[0001] The present invention is directed to novel compounds, to aprocess for their preparation, their use and pharmaceutical compositionscomprising the novel compounds. The novel compounds are useful intherapy, and in particular for the treatment of pain.

BACKGROUND AND PRIOR ART

[0002] The δ receptor has been identified as having a role in manybodily functions such as circulatory and pain systems. Ligands for the δreceptor may therefore find potential use as analgesics, and/or asantihypertensive agents. Ligands for the δ receptor have also been shownto possess immunomodulatory activities.

[0003] The identification of at least three different populations ofopioid receptors (μ, δ and κ) is now well established and all three areapparent in both central and peripheral nervous systems of many speciesincluding man. Analgesia has been observed in various animal models whenone or more of these receptors has been activated.

[0004] With few exceptions, currently available selective opioid δligands are peptidic in nature and are unsuitable for administration bysystemic routes. One example of a non-peptidic δ-agonist is SNC80(Bilsky E. J. et al., Journal of Pharmacology and ExperimentalTherapeutics, 273(1), pp. 359-366 (1995)). There is however still a needfor selective δ-agonists having not only improved selectivity, but alsoan improved side-effect profile.

[0005] Thus, the problem underlying the present invention was to findnew analgesics having improved analgesic effects, but also with animproved side-effect profile over current μ agonists, as well as havingimproved systemic efficacy.

[0006] Analgesics that have been identified and are existing in theprior art have many disadvantages in that they suffer from poorpharmacokinetics and are not analgesic when administered by systemicroutes. Also, it has been documented that preferred δ agonist compounds,described within the prior art, show significant convulsive effects whenadministered systemically.

[0007] We have now found that certain compounds not specificallydisclosed by, but included within the scope of WO 97/23466, exhibitsurprisingly improved δ-agonist properties and in vivo potency.

OUTLINE OF THE INVENTION

[0008] The novel compounds according to the present invention aredefined by the formula I

[0009] wherein

[0010] R¹ is selected from any one of

[0011] where each R¹ heteroaromatic ring may optionally andindependently be further substituted by 1, 2 or 3 substituents selectedfrom straight and branched C₁-C₆ alkyl, NO₂, CF₃, C₁-C₆ alkoxy, chloro,fluoro, bromo, and iodo. The substitutions on the heteroaromatic ringmay take place in any position on said ring systems;

[0012] A preferred embodiment of the present invention is a compoundaccording to FIG. 1 wherein R¹ is as defined above and each R¹ phenylring and R¹ heteroaromatic ring may independently be further substitutedby a methyl group.

[0013] A more preferred embodiment of the present invention is acompound according to FIG. 1 wherein R₁ is pyridinyl, thienyl orfuranyl.

[0014] Within the scope of the invention are also separate enantiomersand salts of the compounds of the formula I, including salts ofenantiomers.

[0015] Separation of racemic mixtures into separate enantiomers is wellknown in the art and may be accomplished for example by separation on asuitable chiral chromatography column. Preparation of salts is wellknown in the art, and may be accomplished for example by mixing acompound of formula I in a suitable solvent with the desired protic acidand isolation by means standard in the art. Salts of compounds offormula I include pharmaceutically acceptable salts and alsopharmaceutically unacceptable salts.

[0016] When the heteroaromatic ring(s) are substituted, the preferredsubstituents are selected from anyone of CF₃, methyl, iodo, bromo,fluoro and chloro.

[0017] Key reaction step Scheme 1, vide infra, is performed by reactingan intermediate compound of the general formula II

[0018] wherein R is an N-protecting group such as Boc or CBz, and P is aO-protecting group such as TBS or Me, which is first N-deprotected andthen alkylated using either,

[0019] i) a compound of the general formula R¹—CH₂—X, wherein R¹ is asdefined above and X is halogen, preferably bromide, and a suitable base,or

[0020] ii) a compound of the general formula R¹—CHO, wherein R¹ is asdefined above, and a suitable reducing agent to give the compounds ofgeneral formula I, after O-deprotection.

[0021] Suitable bases to be used in the standard alkylation step i)above includes, but is not limited to, triethylamine and potassiumcarbonate.

[0022] Suitable reducing agents to be used in the standard reductionstep ii) includes, but is not limited to, sodium cyanoborohydride andsodium triacetoxyborohydride.

[0023] The novel compounds of the present invention are useful intherapy, especially for the treatment of various pain conditions such aschronic pain, neuropathic pain, acute pain, cancer pain, pain caused byrheumatoid arthritis, migraine, visceral pain etc. This list shouldhowever not be interpreted as exhaustive.

[0024] Compounds of the invention are useful as immunomodulators,especially for autoimmune diseases, such as arthritis, for skin grafts,organ transplants and similar surgical needs, for collagen diseases,various allergies, for use as anti-tumour agents and anti viral agents.

[0025] Compounds of the invention are useful in disease states wheredegeneration or dysfunction of opioid receptors is present or implicatedin that paradigm. This may involve the use of isotopically labelledversions of the compounds of the invention in diagnostic techniques andimaging applications such as positron emission tomography (PET).

[0026] Compounds of the invention are useful for the treatment ofdiarrhoea, depression, anxiety, urinary incontinence, various mentalillnesses, cough, lung oedema, various gastro-intestinal disorders,spinal injury and drug addiction, including the treatment of alcohol,nicotine, opioid and other drug abuse and for disorders of thesympathetic nervous system for example hypertension.

[0027] Compounds of the invention are useful as an analgesic agent foruse during general anaesthesia and monitored anaesthesia care.Combinations of agents with different properties are often used toachieve a balance of effects needed to maintain the anaesthetic state(eg. amnesia, analgesia, muscle relaxation and sedation). Included inthis combination are inhaled anaesthetics, hypnotics, anxiolytics,neuromuscular blockers and opioids.

[0028] Also within the scope of the invention is the use of any of thecompounds according to the formula I above, for the manufacture of amedicament for the treatment of any of the conditions discussed above.

[0029] A further aspect of the invention is a method for the treatmentof a subject suffering from any of the conditions discussed above,whereby an effective amount of a compound according to the formula Iabove, is administered to a patient in need of such treatment.

[0030] A further aspect of the present invention is intermediates of thegeneral formula II,

[0031] wherein R is an N-protecting group such as Boc or CBz, and P is aO-protecting group such as TBS or Me.

[0032] Methods of Preparation

[0033] The compounds according to the present invention may be preparedby following any one of the procedures described in Schemes I, II, IIIand IV below. Similar procedures are described in J. March, AdvancedOrganic Chemistry, 4^(th) Edition, John Wiley and sons (1992);Katritsky, A. R., Lan, X Chem. Soc. Rev., pp. 363-373 (1994), which arehereby incorporated by reference.

EXAMPLES

[0034] The invention will now be described in more detail by thefollowing Examples, which are not to be construed as limiting theinvention.

Example 1

[0035] Preparation ofN,N-diethyl-4-[[4-(2-furylmethyl)-1-piperazinyl](3-hydroxyphenyl)methyl]benzamide(compound 7)

[0036] (i) Preparation of 3-{[tert-butyl(dimethyl)silyl]oxy}benzaldehyde(compound 2)

[0037] 3-Hydroxybenzaldehyde (10 g, 82 μmmol) was dissolved in DMF (50mL) with imidazole (12 g, 180 mmol) and t-butyldimethylsilyl chloride(13 g, 90 mmol) and stirred at 25° C. for 12 h. Aqueous workup andchromatography on silica gave compound 2 (18 g, 93%).

[0038] MS (EI) m/e 236, 179, 151.

[0039] (ii) Preparation of4-[(3-{[tert-butyl(dimethyl)silyl]oxy}phenyl)(hydroxy)methyl]-N,N-diethylbenzamide(compound 4)

[0040] N,N-Diethyl-4-iodobenzamide (3.0 g, 10 mmol) was dissolved in THF(100 mL) and cooled to −78° C. under nitrogen atmosphere. n-BuLi (7.7mL, 1.3 M solution in hexane, 10 mmol) was added dropwise during 10 minat −65 to −78° C. Compound 2 prepared in the previous step (1.9 g, 8.0mmol) was added dropwise dissolved in THF (2 mL). NH₄Cl (aq.) was addedafter 30 min. After concentration in vacuo, extraction with EtOAc/water,drying (MgSO₄) and evaporation of the organic phase, the residue waspurified by chromatography on silica to give compound 4 (2.0 g, 60%).

[0041]¹H NMR (CDCl₃) δ 0 (s, 6H), 0.80 (s, 9H), 0.9-1.2 (m, 6H), 2.6 (s,1H), 3.0-3.5 (m, 4H), 5.59 (s, 1H), 6.55-7.25 (m, 8H).

[0042] (iii) Preparation of4-[(3-{[tert-butyl(dimethyl)silyl]oxy}phenyl)(1-piperazinyl)methyl]-N,N-diethylbenzamide(compound 5)

[0043] Compound 4 prepared in the previous step (2.0 g, 4.8 mmol) wasdissolved in dry CH₂Cl₂ (50 mL) and treated with SOCl₂ (0.38 mL, 5.2mmol) in at 0 to 25° C. for 30 min, the solvent was evaporated in vacuo.The residue was dissolved in MeCN (50 mL) and reacted with piperazine(1.6 g, 19 mmol) at 80° C. for 12 h. Concentration in vacuo andchromatography on silica gave compound 5 (1.2 g, 52%).

[0044]¹H NMR (amine, CDCl₃) δ=1.0, 1.1 (2m, 6H), 2.2-2.4 (m, 4H), 2.80(m, 4H), 3.15, 3.45 (2m, 4H), 4.10 (s, 11H), 6.58-7.38 (m, 8H).

[0045] (iv)4-{(3-{[tert-butyl(dimethyl)silyl]oxy}phenyl)[4-(2-furylmethyl)-1-piperazinyl]methyl}-N,N-diethylbenzamide(compound 6)

[0046] 2-furylmethanol (compound 3 prepared as shown in Scheme 1 above)(0.29 mL, 3.3 mmol) was dissolved in CH₂Cl₂ (5 mL) with triethylamine(1.0 mL, 7.4 mmol). Methanesulfonylchloride (0.26 mL, 3.4 mmol) wasadded at 0° C. and the solution stirred 15 min at 0° C. before compound5 prepared in the previous step (0.81 g, 1.7 mmol) was added. Thereaction was stirred 48 h at 25° C. before concentration in vacuo andchromatography on silica gave compound 6 (0.40 g, 42%).

[0047] (v) Preparation ofN,N-diethyl-4-[[4-(2-furylmethyl)-1-piperazinyl](3-hydroxyphenyl)methyl]benzamide(compound 7)

[0048] Compound 6 prepared in the previous step was treated with DMF/2NHCl, 1:2 for 1 h at 25° C. Concentration and reverse phasechromatography gave the title compound 7 (0.26 g, 54%) as theditrifluoroacetate salt.

[0049] MS (ES) 448.24 (MH+monoisot.).

[0050] IR (2×TFA, NaCl): 3232, 1674, 1599, 1457, 1288,1199, 1134 (cm-1).

[0051]¹H NMR (2×TFA, CDCl₃) δ=1.1, 1.2 (2m, 6H), 2.5-3.6 (m, 13H), 4.21(s, 2H), 4.28 (s, 1H), 6.44-7.50 (m, 11H).

Example 2

[0052] Preparation ofN,N-diethyl-4-{(3-hydroxyphenyl)[4-(2-thienylmethyl)-1-piperazinyl]methyl}benzamideditrifluoroacetate (compound 11)

[0053] Prepared as in Example Iiv and Iv from compound 5 as prepared inExample Iiii above, to give the title compound 11, after purification byreverse phase chromatography and extraction (CH₂Cl₂/K₂CO₃(aq)), asbase(28 mg, 31%).

[0054] MS (ES) 464.10 (MH+monoisot.).

[0055] IR (2×TFA, NaCl): 3393, 3180, 1672,1607, 1457, 1289,1199, 1133(cm-1).

[0056]¹H NMR (2×HCl, CDC13) δ=1.1, 1.3 (m, 6H), 2.4-3.6 (m, 13H), 4.27(s, 1H), 4.35 (s, 2H), 6.64-7.45 (m, 11H).

Example 3

[0057] Preparation ofN,N-diethyl-4-{(3-hydroxyphenyl)[4-(3-thienylmethyl)-1-piperazinyl]methyl}benzamidedihydrochlodride (compound 9)

[0058] Prepared as in Example Iiv and Iv from compound 5 as prepared inExample Iiii above, to give the title compound 8, after purification byreverse phase chromatography and extraction (CH₂Cl₂/K₂CO₃(aq)), as base(29 mg, 52%). Treatment with HCl (aq.) gave dihydrochloride. MS (ES)464.08 (MH+monoisot.).

[0059] IR (2×HCl, NaCl): 3393, 3180, 1607, 1457, 1289 (cm-1).

[0060]¹H NMR (2×HCl, CDCl₃) δ=1.1, 1.2 (m, 6H), 1.6-2.2 (m, 8H), 3.1-4.4(m, 5H), 4.30 (s, 2H), 5.0 (s, 1H), 6.8-7.9 (m, 11H).

[0061] Pharmaceutical Compositions

[0062] The novel compounds according to the present invention may beadministered orally, intramuscularly, subcutaneously, topically,intranasally, intraperitoneally, intrathoracially, intravenously,epidurally, intrathecally, intracerebroventricularly and by injectioninto the joints.

[0063] A preferred route of administration is orally, intravenously orintramuscularly.

[0064] The dosage will depend on the route of administration, theseverity of the disease, age and weight of the patient and other factorsnormally considered by the attending physician, when determining theindividual regimen and dosage level as the most appropriate for aparticular patient.

[0065] For preparing pharmaceutical compositions from the compounds ofthis invention, inert, pharmaceutically acceptable carriers can beeither solid or liquid. Solid form preparations include powders,tablets, dispersible granules, capsules, cachets, and suppositories.

[0066] A solid carrier can be one or more substances which may also actas diluents, flavoring agents, solubilizers, lubricants, suspendingagents, binders, or tablet disintegrating agents; it can also be anencapsulating material.

[0067] In powders, the carrier is a finely divided solid which is in amixture with the finely divided active component. In tablets, the activecomponent is mixed with the carrier having the necessary bindingproperties in suitable proportions and compacted in the shape and sizedesired.

[0068] For preparing suppository compositions, a low-melting wax such asa mixture of fatty acid glycerides and cocoa butter is first melted andthe active ingredient is dispersed therein by, for example, stirring.The molten homogeneous mixture is then poured into convenient sizedmolds and allowed to cool and solidify.

[0069] Suitable carriers are magnesium carbonate, magnesium stearate,talc, lactose, sugar, pectin, dextrin, starch, tragacanth, methylcellulose, sodium carboxymethyl cellulose, a low-melting wax, cocoabutter, and the like.

[0070] Salts include, but are not limited to pharmaceutically acceptablesalts. Examples of pharmaceutically acceptable salts within the scope ofthe present invention include: acetate, benzenesulfonate, benzoate,bicarbonate, bitartrate, bromide, calcium acetate, camsylate, carbonate,chloride, citrate, dihydrochloride, edetate, edisylate, estolate,esylate, fumarate, glucaptate, gluconate, glutamate,glycollylarsanilate, hexylresorcinate, hydrabamine, hydrobromide,hydrochloride, hydroxynaphthoate, isethionate, lactate, lactobionate,malate, maleate, mandelate, mesylate, methylbromide, methylnitrate,methylsulfate, mucate, napsylate, nitrate, pamoate (embonate),pantothenate, phosphate/diphosphate, polygalacturonate, salicylate,stearate, subacetate, succinate, sulfate, tannate, tartrate, teoclate,triethiodide, benzathine, chloroprocaine, choline, diethanolamine,ethylenediamine, meglumine, procaine, aluminium, calcium, lithium,magnesium, potassium, sodium, and zinc. Examples of pharmaceuticallyunacceptable salts within the scope of the present invention include:hydroiodide, perchlorate, and tetrafluoroborate. Preferredpharmaceutically acceptable salts are the hydrochlorides, sulfates andbitartrates. The hydrochloride and sulfate salts are particularlypreferred.

[0071] The term composition is intended to include the formulation ofthe active component with encapsulating material as a carrier providinga capsule in which the active component (with or without other carriers)is surrounded by a carrier which is thus in association with it.Similarly, cachets are included.

[0072] Tablets, powders, cachets, and capsules can be used as soliddosage forms suitable for oral administration.

[0073] Liquid from compositions include solutions, suspensions, andemulsions. Sterile water or water-propylene glycol solutions of theactive compounds may be mentioned as an example of liquid preparationssuitable for parenteral administration. Liquid compositions can also beformulated in solution in aqueous polyethylene glycol solution.

[0074] Aqueous solutions for oral administration can be prepared bydissolving the active component in water and adding suitable colorants,flavoring agents, stabilizers, and thickening agents as desired. Aqueoussuspensions for oral use can be made by dispersing the finely dividedactive component in water together with a viscous material such asnatural synthetic gums, resins, methyl cellulose, sodium carboxymethylcellulose, and other suspending agents known to the pharmaceuticalformulation art.

[0075] Preferably the pharmaceutical compositions is in unit dosageform. In such form, the composition is divided into unit dosescontaining appropriate quantities of the active component. The unitdosage form can be a packaged preparation, the package containingdiscrete quantities of the preparations, for example, packeted tablets,capsules, and powders in vials or ampoules. The unit dosage form canalso be a capsule, cachet, or tablet itself, or it can be theappropriate number of any of these packaged forms.

[0076] Biological Evaluation

[0077] In Vitro Model

[0078] Cell Culture

[0079] A. Human 293S cells expressing cloned human μ, δ, and κ receptorsand neomycin resistance were grown in suspension at 37° C. and 5% CO₂ inshaker flasks containing calcium-free DMEM10% FBS, 5% BCS, 0.1% PluronicF-68, and 600 μg/ml geneticin.

[0080] B. Mouse and rat brains were weighed and rinsed in ice-cold PBS(containing 2.5 mM EDTA, pH 7.4). The brains were homogenized with apolytron for 15 sec (mouse) or 30 sec (rat) in ice-cold lysis buffer (50mM Tris, pH 7.0, 2.5 mM EDTA, with phenylmethylsulfonyl fluoride addedjust prior use to 0.5MmM from a 0.5M stock in DMSO:ethanol).

[0081] Membrane Preparation

[0082] Cells were pelleted and resuspended in lysis buffer (50 mM Tris,pH 7.0, 2.5 mM EDTA, with PMSF added just prior to use to 0.1 mM from a0.1 M stock in ethanol), incubated on ice for 15 min, then homogenizedwith a polytron for 30 sec. The suspension was spun at 1000 g (max) for10 min at 4° C. The supernatant was saved on ice and the pelletsresuspended and spun as before. The supernatants from both spins werecombined and spun at 46,000 g(max) for 30 min. The pellets wereresuspended in cold Tris buffer (50 mM Tris/Ci, pH 7.0) and spun again.The final pellets were resuspended in membrane buffer ( 50 mM Tris, 0.32M sucrose, pH 7.0). Aliquots (1 ml) in polypropylene tubes were frozenin dry ice/ethanol and stored at −70° C. until use. The proteinconcentrations were determined by a modified Lowry assay with sodiumdodecyl sulfate.

[0083] Binding Assays

[0084] Membranes were thawed at 37° C., cooled on ice, passed 3 timesthrough a 25-gauge needle, and diluted into binding buffer (50 mM Tris,3 mM MgCl₂, 1 mg/ml BSA (Sigma A-7888), pH 7.4, which was stored at 4°C. after filtration through a 0.22 m filter, and to which had beenfreshly added 5 μg/ml aprotinin, 10 μM bestatin, 10 μM diprotin A, noDTT). Aliquots of 100 μl were added to iced 12×75 mm polypropylene tubescontaining 100 μl of the appropriate radioligand and 100 μl of testcompound at various concentrations. Total (TB) and nonspecific (NS)binding were determined in the absence and presence of 10 μM naloxonerespectively. The tubes were vortexed and incubated at 25° C. for 60-75min, after which time the contents are rapidly vacuum-filtered andwashed with about 12 ml/tube iced wash buffer (50 mM Tris, pH 7.0, 3 mMMgCl₂) through GF/B filters (Whatman) presoaked for at least 2 h in 0.1%polyethyleneimine. The radioactivity (dpm) retained on the filters wasmeasured with a beta counter after soaking the filters for at least 12 hin minivials containing 6-7 ml scintillation fluid. If the assay is setup in 96-place deep well plates, the filtration is over 96-placePEI-soaked unifilters, which were washed with 3×1 ml wash buffer, anddried in an oven at 55° C. for 2 h. The filter plates were counted in aTopCount (Packard) after adding 50 μl MS-20 scintillation fluid/well.

[0085] Functional Assays

[0086] The agonist activity of the compounds is measured by determiningthe degree to which the compounds receptor complex activates the bindingof GTP to G-proteins to which the receptors are coupled. In the GTPbinding assay, GTP[γ]³⁵S is combined with test compounds and membranesfrom HEK-293S cells expressing the cloned human opioid receptors or fromhomogenised rat and mouse brain. Agonists stimulate GTP[γ]³⁵ S bindingin these membranes. The EC₅₀ and E_(max) values of compounds aredetermined from dose-response curves. Right shifts of the dose responsecurve by the delta antagonist naltrindole are performed to verify thatagonist activity is mediated through delta receptors.

[0087] Data Analysis

[0088] The specific binding (SB) was calculated as TB-NS, and the SB inthe presence of various test compounds was expressed as percentage ofcontrol SB. Values of IC₅₀ and Hill coefficient (nH) for ligands indisplacing specifically bound radioligand were calculated from logitplots or curve fitting programs such as Ligand, GraphPad Prism,SigmaPlot, or ReceptorFit. Values of K_(i) were calculated from theCheng-Prussoff equation. Mean±S.E.M. values of IC₅₀, K_(i) and n_(H)were reported for ligands tested in at least three displacement curves.Biological data are tabulated on the following page in Table 1. TABLE 1Biological data. HDELTA RAT BRAIN MOUSE BRAIN Ex. # MOLECULAR STRUCTUREHDELTA EC50 % Emax EC50 % EMax EC50 % Emax 1

0.381 0.21 94.84 1.25 130.09 2.6 112.93 2

0.357 0.24 104.62 0.79 120.37 1.16 117.56 3

0.338 0.15 114.45 0.93 128.08 1 122.03

[0089] Receptor Saturation Experiments

[0090] Radioligand K_(δ) values were determined by performing thebinding assays on cell membranes with the appropriate radioligands atconcentrations ranging from 0.2 to 5 times the estimated K_(δ) (up to 10times if amounts of radioligand required are feasible). The specificradioligand binding was expressed as pmole/mg membrane protein. Valuesof K_(δ) and B_(max) from individual experiments were obtained fromnonlinear fits of specifically bound (B) vs. nM free (F) radioligandfrom individual according to a one-site model.

[0091] Determination of Mechano-Allodynia using Von Frey Testing

[0092] Testing was performed between 08:00 and 16:00 h using the methoddescribed by Chaplan et al. (1994). Rats were placed in Plexiglas cageson top of a wire mesh bottom which allowed access to the paw, and wereleft to habituate for 10-15 min. The area tested was the mid-plantarleft hind paw, avoiding the less sensitive foot pads. The paw wastouched with a series of 8 Von Frey hairs with logarithmicallyincremental stiffness (0.41, 0.69, 1.20, 2.04, 3.63, 5.50, 8.51, and15.14 grams; Stoelting, Ill, USA). The von Frey hair was applied fromunderneath the mesh floor perpendicular to the plantar surface withsufficient force to cause a slight buckling against the paw, and heldfor approximately 6-8 seconds. A positive response was noted if the pawwas sharply withdrawn. Flinching immediately upon removal of the hairwas also considered a positive response. Ambulation was considered anambiguous response, and in such cases the stimulus was repeated.

[0093] Testing Protocol

[0094] The animals were tested on postoperative day 1 for theFCA-treated group. The 50% withdrawal threshold was determined using theup-down method of Dixon (1980). Testing was started with the 2.04 ghair, in the middle of the series. Stimuli were always presented in aconsecutive way, whether ascending or descending. In the absence of apaw withdrawal response to the initially selected hair, a strongerstimulus was presented; in the event of paw withdrawal, the next weakerstimulus was chosen. Optimal threshold calculation by this methodrequires 6 responses in the immediate vicinity of the 50% threshold, andcounting of these 6 responses began when the first change in responseoccurred, e.g. the threshold was first crossed. In cases wherethresholds fell outside the range of stimuli, values of 15.14 (normalsensitivity) or 0.41 (maximally allodynic) were respectively assigned.The resulting pattern of positive and negative responses was tabulatedusing the convention, X=no withdrawal; O=withdrawal, and the 50%withdrawal threshold was interpolated using the formula:

50% g threshold=10^((Xf+kδ))/10,000

[0095] where Xf=value of the last von Frey hair used (log units);k=tabular value (from Chaplan et al. (1994)) for the pattern ofpositive/negative responses; and δ=mean difference between stimuli (logunits). Here δ=0.224.

[0096] Von Frey thresholds were converted to percent of maximum possibleeffect (% MPE), according to Chaplan et al. 1994. The following equationwas used to compute % MPE:${\% \quad {MPE}} = {\frac{{{Drug}\quad {treated}\quad {{threshold}(g)}} - {{allodynia}\quad {{threshold}(g)}}}{{{Control}\quad {{threshold}(g)}} - {{allodynia}\quad {{threshold}(g)}}} \times 100}$

[0097] Administration of Test Substance

[0098] Rats were injected (subcutaneously, intraperitoneally,intravenously or orally) with a test substance prior to von Freytesting, the time between administration of test compound and the vonFrey test varied depending upon the nature of the test compound.

[0099] Writhing Test

[0100] Acetic acid will bring abdominal contractions when administeredintraperitoneally in mice. These will then extend their body in atypical pattern. When analgesic drugs are administered, this describedmovement is less frequently observed and the drug selected as apotential good candidate.

[0101] A complete and typical Writhing reflex is considered only whenthe following elements are present: the animal is not in movement; thelower back is slightly depressed; the plantar aspect of both paws isobservable. In this assay, compounds of the present inventiondemonstrate significant inhibition of writhing responses after oraldosing of 1-100μmol/kg.

[0102] (i) Solutions preparation

[0103] Acetic acid (AcOH): 120 μL of Acetic Acid is added to 19.88 ml ofdistilled water in order to obtain a final volume of 20 ml with a finalconcentration of 0.6% AcOH. The solution is then mixed (vortex) andready for injection.

[0104] Compound (drug): Each compound is prepared and dissolved in themost suitable vehicle according to standard procedures.

[0105] (ii) Solutions administration

[0106] The compound (drug) is administered orally, intraperitoneally(i.p.), subcutaneously (s.c.) or intravenously (i.v.)) at 10 ml/kg(considering the average mice body weight) 20, 30 or 40 minutes(according to the class of compound and its characteristics) prior totesting. When the compound is delivered centrally: Intraventricularly(i.c.v.) or intrathecally (i.t.) a volume of 5 μL is administered.

[0107] The AcOH is administered intraperitoneally (i.p.) in two sites at10 ml/kg (considering the average mice body weight) immediately prior totesting.

[0108] (iii) Testing

[0109] The animal (mouse) is observed for a period of 20 minutes and thenumber of occasions (Writhing reflex) noted and compiled at the end ofthe experiment. Mice are kept in individual “shoe box” cages withcontact bedding. A total of 4 mice are usually observed at the sametime: one control and three doses of drug.

1. A compound of the formula I

wherein R¹ is selected from any one of

where each R¹ heteroaromatic ring may independently be furthersubstituted by 1, 2 or 3 substituents selected from straight andbranched C₁-C₆ alkyl, NO₂, CF₃, C₁-C₆ alkoxy, chloro, fluoro, bromo, andiodo, as well as enantiomer and salts and thereof.
 2. A compoundaccording to claim 1, wherein each R¹ heteroaromatic ring mayindependently be further substituted by 1, 2 or 3 substituents selectedfrom methyl, CF₃, chloro, fluoro, bromo, and iodo.
 3. A compoundaccording to claim 1, wherein each R¹ phenyl ring and R heteroaromaticring may independently be further substituted by a methyl group.
 4. Acompound according to claim 1, wherein R¹ is pyridinyl, thienyl orfuranyl.
 5. A compound according to claim 1 or 2, selected from any oneofN,N-diethyl-4-[[4-(2-furylmethyl)-1-piperazinyl](3-hydroxyphenyl)methyl]benzamide;N,N-diethyl-4-{(3-hydroxyphenyl)[4-(2-thienylmethyl)-1-piperazinyl]methyl}benzamide;andN,N-diethyl-4-{(3-hydroxyphenyl)[4-(3-thienylmethyl)-1-piperazinyl]methyl}benzamide.6. A compound according to any of the preceding claims, in form of itshydrochloride, dihydrochloride, sulfate, tartrate, ditrifluoroacetate orcitrate salts.
 7. A process for preparing a compound of formula I,comprising the reaction of, reacting a compound of the general formulaII

wherein R is an N-protecting group, and P is a O-protecting group suchas TBS or Me, which is first N-deprotected and then alkylated usingeither, i) a compound of the general formula R¹—CH₂—X, wherein R¹ is asdefined in claim 1 and X is halogen, and a suitable base, or ii) acompound of the general formula R¹—CHO, wherein R¹ is as defined inclaim 1, and a suitable reducing agent to give the compounds of generalformula I, after O-deprotection.
 8. A compound according claim 1 for usein therapy.
 9. A compound according to claim 8, wherein the therapy ispain management.
 10. A compound according to claim 8, wherein thetherapy is directed towards gastrointestinal disorders.
 11. A compoundaccording to claim 8, wherein the therapy is directed towards spinalinjuries.
 12. A compound according to claim 8, wherein the therapy isdirected to disorders of the sympathetic nervous system.
 13. Use of acompound according to formula I of claim 1 for the manufacture of amedicament for use in the treatment of pain, gastrointestinal disordersor spinal injuries.
 14. A pharmaceutical composition comprising acompound of the formula I according to claim 1 as an active ingredient,together with a pharmacologically and pharmaceutically acceptablecarrier.
 15. A method for the treatment of pain, whereby an effectiveamount of a compound of the formula I according to claim 1 isadministered to a subject in need of pain management.
 16. A method forthe treatment of gastrointestinal disorders, whereby an effective amountof a compound of the formula I according to claim 1, is administered toa subject suffering from said gastrointestinal disorder.
 17. A methodfor the treatment of spinal injuries, whereby an effective amount of acompound of the formula I according to claim 1, is administered to asubject suffering from said spinal injury.
 18. A compound of the generalformula II

wherein R is an N-protecting group such as Boc or CBz, and P is aO-protecting group such as TBS or Me.